An intermediate tap for a field winding of a motor is desirable for several reasons. Such a tap may be used as a means for changing the motor speed, for example. Additionally, an intermediate tap may be used to provide an output voltage which may be used to activate a lamp or other indicator, to supply power to electronic circuitry, or the like.
In the prior art it has been known to provide contacts to end terminals of a field winding by providing a specialized harness, including four rectangular cavities having cross slots for receiving the terminal ends of each of the two magnet wires. Such a structure is disclosed in Neroda et al., U.S. Pat. No. 4,322,647. Therein, a terminal, or solderless connector, is inserted into each of the four cavities. The connector includes slots aligned with the cross slots of the cavity. The terminal slots are constructed to strip insulating material from the magnet wire, thus to make a permanent electrical connection therewith.
However, such a structure cannot, of itself, provide any connection to intermediate points along the field wire.
A similar molded end coil insulator, including therein terminal supports for the four wire terminals, is disclosed in McCoy U.S. Pat. No. 4,340,829. Loforese U.S. Pat. No. 4,481,435 discloses a friction mounted field coil terminal connector, including upwardly extending, rectangular cross-sectioned, notched connecting wells for securing the four terminal ends of the windings of a field coil.
Other techniques are known for terminating the winding wires (magnet wires) of an electric motor, as illustrated by Hildebrandt U.S. Pat. No. 4,585,964 and Wrobel U.S. Pat. No. 4,673,834.
The prior art fails, however, to disclose any method or system for making electrical contact to a point intermediate the terminals of a field winding, without terminating (or severing) the wire and thus breaking the electrical continuity thereof.
A separate technique is known for making contact with points along an armature winding by providing a connection to a loop of the winding. For example, in Miller Reissue Pat. No. 27,893 it is disclosed that, for an automatically wound armature, anchored leads may be formed between the coils, wherein a length of wire is coursed through a slot adjacent the pairs of slots in which the coil is wound either just before or just after the lead loop or the commutator connection is made. It is recognized therein, however, that such contacts are difficult to make and, accordingly, an improved armature winding pattern is disclosed for tang type connections. However, unless such a specialized winding pattern is used, the connection cannot be easily made, by automatic winding equipment.
Accordingly, when it has been desired to make contact with an intermediate point along a field winding, one approach of the prior art has been to make a tap wire connection to a magnet wire located on the field coil. Such an approach, however, hampers the cooling of the coil in view of the added materials placed directly on the coil and connected thereto.
Alternatively, it has also been the practice of the prior art to provide an intermediate winding tap by stopping operation of a coil winding device and by extending a pawl to engage a long loop of wire (as long as 4 to 6 inches in length) to extend the loop away from the field. Such an approach, however, requires that the added length of magnet wire be fixedly fastened to the structure in a separate processing step. Moreover, upon completion of the winding, the long loop needs to be manually cut to the desired length and the appropriate contact then must be made to the cut loop.
However, such an approach suffers from a number of deficiencies. Of necessity, the winding process is slowed while the loop is extended. Additional labor is required to fasten the loop as well as to cut the loop to length and to make the appropriate contact. Further, because a large loop is pulled from the winding and subsequently cut off, additional wire must be used for the winding. Each of the above factors increases the cost of producing a winding having an intermediate tap. Moreover, because the loop is cut, continuity of current through the winding is impaired, and reliability of such windings deteriorates.